Azo pigment



Patented Oct. 31, 1944 UNITED STAT A zo PIGMENT,

William B. Reynolds, Chicago, 111., assignor to Interchemical Corporation, New York; N. Y., a

corporation of Ohio No Drawing. Application February 25, 1942,

Serial No. 432,243

1 Claim.

This invention relates to a new insoluble deep yellow dyestuff, or pigment, which is obtainable by coupling tetrazotized 3,3'-dichlorbenzidine with aceto-acet-p-toluidide, and which is especially useful in printing inks and printing emul- SlOIlS.

Many insoluble dyestuffs, or pigments, have been made heretofore by coupling various azotized benzidines with aceto-acetarylamides, and these compounds are generally referred to as the benzidine yellows or oranges because of their characteristic yellow to orange colors. Although the known compounds are often used in various printing and dyeing operations in preference to other types of yellow dyestuiis (such as the Hansa yellows) because of their relatively superior solvent fastness and greater tinctorialstrength, they are not used where it is important to maintain the particular shade of color over long periods of time in exposed places because of their notably poor lightfastness.

This invention provides a deep yellow pigment of the class of benzidine yellows which is distinguished from known pigments of the same class by its superior lightfastness and high coloring strength, or tinctorial power.

The pigment of this invention may be designated as the compound resulting from the coupling of tetrazotized 3,3-dichlorbenzidine with The pigment of this invention may be mad in the usual manner from 3,3'-dichlorbenzidine and aceto-acet-p-toluidide, and if the latter is not available it, in turn, may be made from acetoacetic ester and the corresponding amine base. Other well known chemical reactions may be employed if desired. The following examples are, however, illustrations of one specific method of preparing the pigment.

Example 1 2.2 mols of ethyl aceto-acetate previously dried over anhydrous sodium sulfate and soda ash, and 325 parts by weight of anhydrous xylene were placed in a flask and heated to gentle reflux. Then 2 mols of p-toluidide were added to the xylene solution of the aceto-acetic ester over a period of about 45 minutes. The alcohol formed in the reaction was removed by distillation. By maintaining sufiicient reflux the alcohol may be removed quantitatively as the reaction proceeds. After all of the amine was added the heatin was continued for 15 or 20 minutes or until the theoretical amount of alcohol had been distilled from the reaction mixture. On completion of the reaction the mixture was cooled and poured into parts of 10 N hydrochloric acid containing 300 parts of ice, whereupon the aceto-acet-p-toluidide was precipitated. After stirring for 15 minutes the anilide was separated by filtration and the cake pressed to remove as much as possible of the xylene and excess aceto-acetic ester. The crude anilide was then dissolved in 2500 parts of water r containing 2 mols of caustic soda, clarified with 5 parts each of activated silica and activated carbon, and filtered. The filtrate was iced to about 5 C. and the anilide precipitated with hydrochloric acid, filtered, washed acid-free to Congo red and dried in a low temperature oven.

Example 2 The tetrazo compound was made in the following manner.

One mol of 3,3'-dichlorbenzidine was stirred into 2000 parts by weight of water and 5 mols of 10 N hydrochloric acid were added. The mixture was stirred for 2 hours and 5000 parts of ice were added, along with 20,000 parts of water. The resulting slurry was stirred until the temperature of the liquid dropped below- 5" 0. Then 2 mols of sodium nitrite, dissolved in 2000 parts of Water, were added rapidly to the slurry. Afterstirring for 45 minutes, while maintaining an excess of sodium nitrite, the tetrazo solution was clarified with activated carbon and silica.

A couplingslurry of the anilide of Example 1.

was prepared by dissolving 2.06 mols of the anilide in 7000 parts of water containing 2.1 mols of caustic soda and 1000 parts of ice. Then 6 mols of sodium acetate were added and the mixture stirred until complete solution was obtained. After clarifying, 2.1 mols of 2 N hydrochloric acid were slowly added, yielding a white slurry which was slightly acid to litmus.

andm

aceto-acet-meta xylidide, respectively. All of these products have found wide commercial ap-' plication; The pigment of thisinvention isvredtder in shade than the o-toluidide product but it is much faster to light than either this product or the meta, xylidide product. It isespecially fast in long tints, such as when extended with: zinc V oxide, and it is equal in stength, or tinctorial value, to the o-toluidide product. The new com pound is non-bleeding in oils and most solvents, so that it is especially suited for use as a pigment in color printing inks, textile printing emulsions and the like.

I claim: A compound having the formula CH3 on, a 01 c1 1 t .NH llIH WILLIAM B. REYNOLDS. 

